Patent GB-190722399-A (GB)
Title: Improvements in Valves for Air-brakes.
Inventor: JOHNSON ANDREW THOMAS
Filed: 1907-10-10
Granted: 1908-08-20
Abstract: 22,399. Johnson, A. T. Oct. 10. Brakes.-A pressure-reducing valve is placed in the branches of the train-pipe leading to the triple valves on the vehicles, and is provided with a cock for cutting out the reducing valve on heavily loaded cars so as to obtain full braking pressure, the valve also serving to produce local venting of the train-pipe during emergency applications. The valve comprises a casing with two compartments 1, 2, Fig. 1, of unequal diameter, and pistons 3, 4 secured to a spindle 5 which actuate slide valves 6, 9. A passage 7 controlled by the valve 6 leads from the upper side of the smaller piston 3 to the underside of the large piston. When the valve is empty, the port 7 is closed by the slide 6, the movable parts being centred by springs 17, 18, and as air is admitted from the main reservoir the piston 3 is depressed into the charging position shown in Fig. 1 and allows air to pass to the brake parts until the pressure on the larger piston 4 overcomes the pressure on the smaller piston and closes the feed-port 7. 1 he valve 6 also controls an exhaust part 8, and the valve 9 controls a small exhaust port 10 and a larger port 11. When the train-pipe pressure on the piston 3 is reduced to apply the brakes for a service application, the piston 4 is raised by the pressure of the air in the compartment 2 and moves the valve 9 to uncover gradually the small exhaust port 10. The reduction of pressure in the compartment 2 and its connected parts operates the triple valve for a service application of the brakes, the port 10 being closed as soon as the pressures on the pistons 3, 4 balance. When a large reduction of pressure occurs in the train-pipe, the pistons move the slide valves 6, 9 to uncover the large exhaust ports 8, 11. In this position the pressure in the compartment 2 is reduced sufficiently rapidly to cause the triple valve to move to emergency position, and the train-pipe is exhausted through the port 8. This prevents the valves from moving to. lap position until the pressure is exhausted from both compartments 1, 2 and allows a full application of the brakes. If, in a service application, a defective triple valve moves to emergency position, the sudden decrease of pressure on the piston 4 causes the pistons to move into the position shown in Fig. 1 so as to open the feedport 7 to increase the pressure in the compartment 2 and release the triple valve. The area of the feed-port 7 is not large enough to allow the air to flow through it sufficiently rapidly to move the other triple valves to emergency position. By turning the cock 13, the reducing-valve is cut out, the air at full reservoir pressure being supplied through a passage 12 in the valve casing to the triple valve. In a modified form, shown in Fig. 7, in order to obtain a local venting of the train-pipe when the pressure-reducing valve is cut out by the cocks 24, 13, the passage 12 is enlarged and contains a piston 23 controlling two slide valves 26, 29 which operate similarly to the valves 6, 9 to control a train-pipe exhaust port 28 and exhaust ports 30, 31 corresponding to the exhaust ports 8, 10, 11 before described.